Effect of transition metal substitution on high-temperature properties of thermoelectric materials

Download

index.pdf

Date

2014

Author

Güneş, Murat

Metadata

Show full item record

Item Usage Stats

172
views

61
downloads

The objective of the present dissertation is to improve the thermoelectric efficiency (ZT) of Ca3Co4O9 metal oxide with a focus on nanostructuring, porosity and elemental substitution altering the electrical and thermal transport properties at high temperature and to establish a unique high temperature Seebeck coefficient and electrical resistivity measurement system. An instrument for the high temperature measurement of Seebeck coefficient and electrical resistivity of one and/or two bulk samples over a temperature range of 300 – 1100 K is designed and implemented in our laboratory. During the installation of the system, five inventions have been made. These are; 1) cold-finger effect eliminated triple beadless thermocouples, 2) magnetic field and furnace eliminated micro-heaters, 3) differential temperature measurement specialty, 4) two-sample simultaneous measurement feature 5) non-destructive axial four-point probe electrical resistivity measurement conduction. Due to the above mentioned major accomplishments, while cost and size is reduced, measurement accuracy and sensitivity is further enhanced. The total estimated data error for the Seebeck coefficient and resistivity measurements is less than 2.6 % and 1 %, respectively. In order to investigate the effect of nanostructuring and porosity on thermoelectric properties of Ca3Co4O9 oxide, samples of the material are synthesized via citrate sol-gel method with different average grain sizes ranging from 18, 30, 68 nm and 2 m. A considerable increase in electrical resistivity is observed, however, Seebeck coefficient is not much suppressed. It is investigated that thermal conductivity is substantially lower for nano-sized samples due to grain boundary scattering. Porosity further contributes to reducing this value leading to increase in the density of scattering regions. Thermal conductivity is decreased by 23 % with the help of nanostructuring and porosity. The enhancement of ZT value is 61 % and it reaches 0.29 at 1000 K for 18 nm sample. Polycrystalline Ca3-xCrxCo4O9 (x = 0.0, 0.01, 0.03, 0.05 and 0.07) thermoelectric samples are prepared. Cr substitution to Ca-site leads to the spin-entropy enhancement and this caused increase in the Seebeck coefficient with up to x = 0.03 Cr substitution. Power factor is enhanced by 30 %. The thermoelectric performance is the most significant in x = 0.03 sample with ZT value of 0.26 at 1100 K. The enhancement in ZT value is 33 %.

Subject Keywords

Thermoelectric materials., Transition metals., Porosity., Nanostructures., Nanotechnology.

URI

http://etd.lib.metu.edu.tr/upload/12618123/index.pdf
https://hdl.handle.net/11511/23946

Collections

Graduate School of Natural and Applied Sciences, Thesis

Suggestions

OpenMETU
Core

Effect of Presoaked Expanded Perlite Aggregate on the Dimensional Stability and Mechanical Properties of Engineered Cementitious Composites KESKİN, SÜLEYMAN BAHADIR; Sulaiman, Kamaran; Sahmaran, Mustafa; Yaman, İsmail Özgür (American Society of Civil Engineers (ASCE), 2013-06-01) This paper reports on an investigation of the use of expanded perlite aggregate as saturated lightweight aggregate (LWA) with respect to the mechanical and dimensional stability properties of engineered cemetitious composites (ECC). Expanded perlite aggregate was soaked in water for 24 h before its use in ECC, and replaced 10, 20, and 30% of the aggregate that was used in ECC production. The mixture proportion of a standard ECC mixture with properties that have been extensively reported in the literature is...
Effect of surface treatment on electrical conductivity of carbon black filled conductive polymer composites Koysuren, Ozcan; Yesil, Sertan; Bayram, Göknur (Wiley, 2007-06-05) Two different types of surface modifiers, 3-aminopropyltriethoxysilane and formamide, were applied to carbon black (CB) particles to lower electrical resistivity of polymer composites prepared by treated CB. Two different matrices, low-density polyethylene and nylon 6, were chosen to compound with surface modified CB. Surface energy of CB was increased by adding amine or amide functional groups during surface treatment of CB. According to electron spectroscopy for chemical analysis (ESCA), chemical modifica...
Effect of Boron Phosphate on the Mechanical, Thermal and Fire Retardant Properties of Polypropylene and Polyamide-6 Fibers DOĞAN, Mehmet; Bayramlı, Erdal (Springer Science and Business Media LLC, 2013-10-01) The effect of boron phosphate (BPO4) nanoparticles on the mechanical, thermal, and flame retardant properties of polypropylene (PP) and polyamide 6 (PA-6) fibers are investigated by tensile testing, thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), and micro combustion calorimeter (MCC). The addition of BPO4 reduces the mechanical properties of the both PP and PA-6 fibers. According to the TGA results, the addition of BPO4 does not change the thermal behavior of PP fiber and slightl...
Effect of metal oxide on light oil combustion - TA and kinetic analysis Kök, Mustafa Verşan (Springer Science and Business Media LLC, 2003-01-01) Simultaneous thermogravimetry (TG) and differential thermal analysis (DTA) were applied to light crude oil combustion in the presence and absence of metal oxide. In crude oil-limestone mixture, three main transitional stages are detected. These are distillation, low-temperature oxidation (LTO) and high temperature oxidation (HTO) regions respectively. In the case of experiments with Fe(III)chloride at different amounts, the shape of TG-DTA curve is changed considerably. Kinetic parameters of the samples are...
Effect of amorphous SiC layer on electrical and optical properties of Al/a-SiC/c-Si Schottky diode for optoelectronic applications Barbouche, M.; Benabderrahmane Zaghouani, R.; Ben Ammar, N.E.; Aglieri, V.; Nasser, H.; Turan, Raşit; Ezzaouia, H. (2021-01-01) In this work, we report on the study of the electrical and optical properties of amorphous silicon carbide (a-SiC)-based Schottky diodes for optoelectronic applications. A significant decrease of reflectivity and an enhancement of the passivating properties of more than 97% were reached after a-SiC layer deposition on silicon substrate. The deposited a-SiC film exhibits a dielectric constant of 2.143. Temperature effect on Schottky diode performances was carried out through the analysis of the current–volta...

Citation Formats

M. Güneş, “Effect of transition metal substitution on high-temperature properties of thermoelectric materials,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.